The invention relates to a circuit arrangement for monitoring speed, particularly for fan drives.
Such speed monitoring circuit arrangements are, for example, used in conjunction with fans for cooling electronic computers or other temperature sensitive assemblies. They serve to initiate alarm or switching operations, or both, when the fan stops or the fan speed drops below a predetermined minimum value in order to prevent damage to the assembly to be cooled. In uses of this type, fan failure can lead to significant damage. Therefore, great practical significance is attached to the reliable detection of fan malfunctioning. In other situations, it can be important to reliably determine and indicate that a predetermined maximum speed has been exceeded.